The fermentative production of organic acids results in aqueous culture broths containing dissolved organic acids, microorganisms and impurities essentially consisting of residues of substrates and cell metabolism of said microorganisms.
A traditional method for purifying an organic acid from a fermentation broth consists in forming an insoluble calcium salt of organic acid, by contacting the broth with lime, and then recovering said salt by filtration. The salt of organic acid is then treated by adding sulfuric acid. After a further filtration step, an aqueous solution of organic acid is collected on the one hand, and insoluble gypsum (calcium sulfate) is collected as waste on the on the other hand.
This technique requires large amounts hot water and sulfuric acid, and it leads to the production of large amounts of gypsum waste without market value.
Chromatography-based processes have also been proposed as alternative solutions, offering reduced operation costs and requiring less effluent treatment. Document FR 2900654 describes such a chromatography-based process for the purification of organic acids. In the chromatographic separation step (also called acid retardation step) of this kind of process, diluted acidic water is used as the eluent. As a result, a raffinate waste stream is produced, which contains mineral acid at a relatively large concentration. Such an acidic effluent raises environmental concerns and is not easy to efficiently treat.
Document FR 3005428 describes a process of recycling a regeneration effluent in an ion exchange process, using electrodialysis. The effluent which is subjected to the electrodialysis treatment contains a high concentration of chloride ions.
There is therefore still a need for efficiently treating and valorizing effluent streams in processes for the production of organic acids.